The present invention relates to a method of fabrication of a semiconductor integrated circuit device; and, more particularly, the invention relates to a technique for improving the quality of pure water to be used for the fabrication of a semiconductor integrated circuit device.
Upon fabrication of a semiconductor device, including microfabrication of an integrated circuit, it is required to remove impurities from the surface or interface of a semiconductor wafer (which will hereinafter simply be called a “wafer”) by cleaning, thereby maintaining the cleanness of the wafer. Foreign matter on a wafer may cause disconnection or short-circuit of wiring. In particular, heavy metal components must be removed completely, because they have a serious influence on the electrical properties of the device.
Pure water is used for washing a wafer surface to remove a chemical solution after the wafer has been cleaned therewith or wet etched therewith, thereby making the wafer clean; or pure water is used for preparing a chemical solution used in a cleaning or wet etching step. Pure water used in such a step is prepared by removing, from raw water, fine particles, organic matter and high molecular ions by use of an RO (reverse osmosis) unit equipped with an RO (Reverse Osmosis) membrane, removing the other ions by using an ion exchange resin, and then removing fine particles and living bacteria, which are still in the raw water after the action of the RO unit and ion exchange resin, using UF equipment (ultrafiltration equipment). A process for preparation of such pure water is disclosed, for example, in Japanese Unexamined Patent Application No. Hei 4(1992)-78483. Also, Japanese Unexamined Patent Application No. Hei 10(1998)-216721 discloses a technique for removing anions, which are too small to pass through UF equipment, using an anion adsorption membrane apparatus disposed downstream of the UF equipment.